1. Field of the Invention
The present invention relates to a continuous sheet guide mechanism for guiding a continuous sheet in winding a continuous sheet around the platen of a serial printer and setting the continuous sheet on the tractors of the serial printer.
2. Description of the Prior Art
Referring to FIG. 5 showing the arrangement of conventional tractor units 5 by way of example, on a serial printer, a support shaft 3 is supported on and fixed with screws to side frames 1 and 2, and a driving shaft 4 is journaled for rotation on the side frames 1 and 2. The side frames 1 and 2 are secured to the side frames 7 and 8 of the serial printer, respectively, by locking means, not shown. The pair of pin tractor units 5 are supported slidably on the support shaft 3 on the right and left sides thereof, respectively. A sheet guide member 6 is supported slidably on the support shaft 3 in the middle of the interval between the pin tractor units 5. A platen 9 extends in front of and in parallel to the driving shaft 4. A print head 10 and a ribbon cassette 11 are disposed in front of the platen 9.
Referring to FIG. 6, each tractor unit 5 for guiding a continuous sheet 12 can be fixed at an optional position on the support shaft 3 by means of a locking lever 13. Each of the tractor units 5 has a guide section 14 for guiding the continuous sheet 12 introduced into the serial printer through a sheet inlet opening 15. Each of the tractor units 5 has a driving wheel 16 mounted slidably on the driving shaft 4 for rotation together with the driving shaft 4 to drive a tractor belt 17 extended between the driving wheel 16 and a wheel mounted slidably and rotatably on the support shaft 3. The tractor belt 17 is provided on the outer surface thereof with pins 17a, which engage perforations formed in each side edge of the continuous sheet 12 to guide the continuous sheet 12.
Referring to FIG. 7, the sheet guide member 6 has a supporting leg 6a projecting downward from an upper part of the top guiding section and slidably engaging the fixed support shaft 3, and a protective leg 6b extending downward from a lower part of the top guiding section so as to protect the driving shaft 4.
In introducing the continuous sheet 12 into the serial printer so as to make the tractor units 5 engage the continuous sheet 12, the front edge of the continuous sheet 12 is inserted through the sheet inlet opening 15 in a direction indicated by an arrow A. The lateral movement of the continuous sheet 12 relative to the platen 9 is restricted by the guiding sections 14 of the tractor units 5. The continuous sheet 12 passes around the platen 9 and advances in a direction indicated by an arrow B while the pins 17a of the tractor belts 17 of the tractor units 5 engage the perforations formed in the opposite side edges of the continuous sheet 12, respectively.
As is obvious from FIG. 7, the conventional sheet guide member 6 is unable to guide the continuous sheet 12 downward relative to the platen 9. Therefore, the front edge of the continuous sheet 12 is liable to hit on the platen 9 at a position P (FIG. 7) and is turned upward in a direction indicated by an arrow C. To prevent such movement of the front edge of the continuous sheet 12, the continuous sheet 12 needs to be depressed by hand in introducing the continuous sheet 12 into the serial printer.